1. Field of the Invention
This invention relates to a structured aqueous based heavy duty liquid detergent formulation containing a suspended bleach along with selected stability enhancers.
Liquid detergent products have become a large segment of the U.S. detergent market. Their market share in the past several years has more than doubled. Currently marketed liquid detergents contain built-in softening in the wash as well as enzymes for added stain removal. No completely formulated liquid detergents however, contain a completely satisfactory bleach.
Liquid bleach adjuncts which are to be added separately to the wash, containing hypochlorite or hydrogen peroxide are established, successful products. A low pH, surfactant-structured liquid containing 1,12 diperoxydodecanedioic acid (DPDA), has been patented by Humphreys et al. in U.S. Pat. No. 4,642,198. A structured aqueous system has been employed in this bleach adjunct but due to the low pH and low amount of surfactant usually employed, the adjunct product cannot be used alone to accomplish washing.
The high concentrations of surfactants which must be included in a fully formulated liquid detergent to clean during the wash generally make it difficult to prepare an appropriately structured liquid. Structuring, however, is necessary to suspend the particulate bleach and, thus, minimize settling and other types of instability. Structured liquids are well known in the art and are described more fully below. Further, the large amount of surfactant required usually increases the viscosity of structured liquids to unacceptable levels. The viscosity, thus, must be decreased to a commercially acceptable level while still retaining the suspending characteristics of the structured liquid.
An additional difficulty is that the suspended bleach particles must not be too soluble in the product or the bleach may react with included organic materials. It is, thus, desirable to further stabilize the bleach by decreasing the pH of the concentrated composition to decrease the solubility of the bleach particles. A low pH, however, is not optimal for washing and, thus, it must be capable of increasing substantially on dilution when the product is used so that normal alkaline wash pH's can prevail.
It was, thus, desireable to formulate an aqueous based heavy duty detergent which contains relatively stable bleach and high levels of surfactant, yet still retains the suspending properties of a structured liquid while incorporating acceptable viscosity characteristics.
2. Description of the Art
One of the early patents is Edwards et al U.S. Pat. No. 3,996,152, disclosing the suspension of diperoxyacids by non-starch thickening agents such as Carbopol 940 in an aqueous media at low pH. Suitable actives were diperazelaic, diperbrassylic, dipersebacic and diperisophthalic acids. Bradley U.S. Pat. No. 4,017,412 reports similar systems except that starch based thickening agents were employed. From later investigations it became evident that the thickener types mentioned in the foregoing patents formed gel-like matrices which exhibited instability upon storage at elevated temperatures. At high concentrations they cause difficulties with high viscosity.
U.S. Patent 4,642,198 (Humphreys et al.) hereby incorporated by reference herein, lists a variety of water-insoluble organic peroxy acids intended for suspension in an aqueous, low pH liquid. This patent disclosed the use of surfactants, both anionic and nonionic, as suspending agents for the peroxy acid particles. The preferred peroxy material was 1,12-diperoxydodecanedioic acid (DPDA).
This art has emphasized optimizing the suspending or thickening chemical components of the liquid bleach to improve physical stability.
EP No. 176,124 to de Jong and Torenbeck discloses a pourable bleach composition containing peroxycarboxylic acid in an aqueous suspension with 0.5 to 15% alkylbenzene sulfonic acid and low levels of sulfate salt.
Neither of the above patents discloses the use of a system which will allow the compositions to be used as effective heavy duty liquid detergents in the main wash. Both compositions must be used with a buffered adjunct (powder or liquid) to ensure the neutral to alkaline pH necessary for general detergency. The decline in detergency with reduced pH is well known in the art and is discussed in Cockrell, U.S. Pat. No. 4,259,201. deJong avoids high surfactant concentrations. Such compositions are said to be excessively thick and difficult to pour. Humphreys claims surfactant concentrations from 2-50%; however, compositions in excess of about 15% may exhibit excessive thickness and Humphrey's pH is too low for commercially acceptable detergency.
There have been many different approaches to the problem of producing an aqueous based heavy duty liquid detergent containing a bleach; however, none of these approaches have been completely satisfactory. In many cases stability has been enhanced at the expense of acceptable viscosity or a low pH has been employed to improve bleach stability by sacrificing alkaline wash pH's.
Accordingly, it is an object of the present invention to provide a fully formulated aqueous based heavy duty liquid detergent composition containing a suspended peroxy bleach. The composition exhibits good stability, acceptable viscosity and good bleaching and cleaning characteristics while substantially eliminating or minimizing many of the problems of the art. Other objects and advantages will appear as the description proceeds.